The cornea is transparent tissue with no blood vessels, a diameter of about 1 cm and a thickness of about 1 mm. The transparency of a cornea has an important influence on visual function. Various physiological and biochemical phenomena of the cornea mainly function to maintain this transparency.
Corneal epithelial defects caused by corneal ulcers, exfoliation of corneal epithelium, keratitis, dry eyes, and various other diseases can be repaired naturally if no mixed infection occurs. However, if repair is delayed or not made for certain reasons, corneal epithelial migration takes place, such that the normal epithelium construction is adversely affected, and the structure and function of the parenchyma and endothelium are also harmed. In prior art, the principal therapy was the so-called passive method, in which the surface of the cornea is protected from external stimulation so that the epithelium again extends naturally to cover the damaged portion. In recent years, with developments in cell biology, factors pertaining to split, movement, fusion, migration, etc., have been clarified, and it has been reported that compounds that can promote corneal epithelial migration play an important role (Ringan, 46, 738–743 (1992); Ganka Shujutsu, 5, 719–727 (1992)).
On the other hand, many authors have reported research on P2Y receptor agonists which are the effective component in the present invention. For example, U.S. Pat. No. 5,292,498 described use of uridine 5′-triphosphate (UTP), adenosine triphosphate (ATP), etc., in maintaining secretion of mucus as a characteristic feature in treating lung diseases. WO 97/29756 stated that UTP or other phosphoric acid nucleoside P2Y receptor agonists are effective in treating tympanitis. WO 98/34593 stated that UTP or other P2Y receptor agonists have a tear secreting function, and can be used in treating dry eyes and diseases of the nasolacrimal duct. However, no research yet exists on the corneal epithelial migration effect of P2Y receptor agonists.
Discovery of new applications of said P2Y receptor agonists is of great interest. Also, in ophthalmology, searching for compounds that can display a corneal epithelial migration promoting effect is a very important topic.